Answer: $1,758.17
Adding the principal paid and interest paid will result in $1,758.17 for every month/column.
For example,
Month 21 - $688.68 + $1,069.49 = $1,758.17
Month 22 - $692.73 + $1, 065.44 = $1,758.17
And so on..
As $1,758.17 is the constant total when you add principal paid and interest paid in every month, that is your answer.
